Thin-profile display devices such as liquid crystal display devices have rapidly spread in recent years, and are widely used for not only televisions but also electronic books, digital photo frames, industrial appliance (IA), personal computers (PCs), tablet PCs, smartphones, and the like. These applications demand a wide variety of performance, and various liquid crystal display modes are developed.
Frequently used liquid crystal display modes include an in-plane switching (IPS) mode and a fringe field switching (FFS) mode in which the liquid crystal molecules having positive or negative anisotropy of dielectric constant are aligned in the direction horizontal to the main surface of a substrate.
Liquid crystal display devices require uniform alignment of the liquid crystal molecules. Examples of alignment treatment of alignment films for aligning the liquid crystal molecules include rubbing and photo-alignment, and rubbing in which the surface of an alignment film is rubbed with a cloth has widely been applied. However, the rubbing causes problems such as foreign-matter defects due to dust of cloth and display unevenness, and breaking of thin film transistor elements due to static electricity generated in rubbing with a cloth. Further, as the definition of the display devices such as tablet PCs and smartphones more and more increases, it becomes more and more difficult to uniformly align the liquid crystal molecules by rubbing, in which the alignment precision is restricted by the density of the pile of a cloth. Thus, in order to solve these problems, photo-alignment has been recently developed in which anisotropy is given to an alignment film by applying light such as UV to generate an anchoring force, instead of the rubbing.
Some documents are known to disclose a method of uniformly aligning the liquid crystal molecules by the aforementioned alignment treatment and thereby preventing display failure (for example, see Patent Literature documents 1 and 2). Some other documents are known to disclose a composition for photo-alignment films containing a photo-reactive compound which increases the degree of freedom of material selection (for example, see Patent Literature 3). Some other documents are known to disclose that main heating during formation of an alignment film improves the orientational order of a polymer (for example, see Non-Patent Literature documents 1 and 5). Still other documents are known to disclose that performing pre-heating, polarized UV irradiation, and main heating in the order set forth improves the orientational order of a polymer (for example, see Non-Patent Literature documents 2 to 4). Non-Patent Literature 4 relates to formation of a photo-alignment film.